In high-voltage power transmission systems there is a need for fast communication between protection and control computers, especially if the system uses closed-loop control of various elements. In order to provide a reliable system it is at the same time a need for redundancy. Many power transmission systems are furthermore provided in various hierarchical levels. There may therefore be a need to provide control and protection computers in corresponding hierarchical levels. A high-voltage power transmission system may therefore also need to be controlled and monitored on various hierarchical levels.
It is known to provide redundant protection and control computers connected to redundant computer communication networks.
One type of system that uses redundant computers on various hierarchical levels for HVDC (High Voltage Direct Current) is the Win-TDC system. Win-TDC is for instance described in “WIN-TDC The State-of-the-Art Control and Protection System for HVDC Applications”, Nicol, B et al., Transmission and Distribution Conference and Exhibition, Asia and Pacific, 2005 IEEE/PES, 2005, page 1-5 and in “Latest Control and Protection Innovations Applied to the Basslink HVDC Interconnector”, Davis M. et al., The 8th IEEE International Conference on AC and DC Power Transmission, 2006 ACDC 2006, 28-31 Mar. 2006, page 30-35. In this system there are redundant computers connected to two redundant LANs in an Operator Control Level and in a Control & Protection Level. Here the Control and Protection level includes redundant station control systems as well as redundant pole control/DC protection systems for two poles. However there is no redundant computer communication network provided between various hierarchical control and protection levels. There is furthermore no discussion in any of the documents on how communication is performed over these redundant LANs.
In “A distributed sequential control system for the Apollo HVDC substation”, Venter, F. et al., AFRICON, 1996, IEEE AFRICON 4th, 24-27 Sep., 1996, page 869-873, Vol. 2 there is described an HVDC substation with dual LANs between a control room including redundant MMIs based on UNIX work stations and redundant CPUs in Station and Pole Control as well as a single CPU in Bridge Control. In the Station and Pole Control an active CPU is connected to one LAN and a standby CPU is connected to the other LAN. The sole CPU in Bridge Control is connected to both LANs. The document also mentions that the sole bridge CPU communicates with both LANs.
The part of a high-voltage power transmission system that is perhaps most important for the reliability of a high-voltage power transmission system is here the part where control and protection is performed. There is therefore room for improvement in the design of this part of the system.
In view of what has been described above there is therefore a need for increasing the reliability of a high-voltage power transmission system.